The primary means by which nerve cells communicate is via the release of neurotransmitter at chemical synapses. The function of the brain and the ability of the brain to store and process information depends on synaptic connections forming precisely and reliably. This proposal is directed towards developing a molecular understanding the mechanisms that regulated this process of synaptogenesis. We propose to use a combination of genetics, cell biology, molecular biology and live imaging to identify and characterize the role of molecular components of the signaling pathways that coordinate synaptic development by studying the specific assembly of a set of nerve-nerve synapses. In previous work, we described the order of cellular events in nascent synapse formation by visualizing the recruitment of fluorescent-tagged components to newly forming synapses. Furthermore, we isolated mutants that disrupt the formation of these synapses. Cloning of a subset of these identified an F-box protein that selectively targets proteins for ubiquitin-mediated degradation, several regulators of the cytoskeleton, a transcriptional regulatory protein and a novel conserved protein. Using a variety of molecular, genetic and protein interaction studies we now propose to determine at a mechanistic level how these proteins function to regulate synapse assembly. In addition, we will use genetic approaches to isolate and characterize additional genes that disrupt signaling between mechanosensory neurons and their synaptic partners in C. elegans to extend our molecular understanding of the process. Together these approaches will help define mechanisms that cells use to identify and communicate with one another during the process of synapse formation and synaptic maintenance. While synaptogenesis is undoubtedly less complex in C. elegans than in vertebrates, it is already clear that similar pathways operate in both systems. Thus, analysis of the molecules participating in the process in C. elegans should help define a set of general and likely conserved principles that are common to synaptogenesis mechanisms in general.